When it comes to expressing affection and making someone smile, sincerity and context matter more than any particular word. Different people have different preferences, so what one person finds endearing, another might not.
With that said, here are a few sweet and affectionate words that are generally well-received in a loving and intimate context:
Beautiful: Complimenting someone's beauty can be a lovely gesture.
Adorable: This word can convey a sense of affection and fondness.
Charming: A compliment that implies attractiveness and charisma.
Gorgeous: Letting someone know that you find them stunning.
Amazing: Acknowledging their unique qualities and presence.
Beloved: An endearing term that conveys a deep affection.
Darling: A classic term of endearment.
Precious: Suggesting that they are cherished and valuable to you.
Enchanting: Implying that you find them captivating and magical.
Remember, the key to making someone smile is genuine and thoughtful communication. Pay attention to the person's reactions and responses, and always treat them with respect and kindness. Different people have different preferences, so always consider what would be most appropriate and appreciated by the individual you are with. Communication in an intimate context should always be consensual and considerate of each other's feelings and boundaries.